Revert "getParameterSetNames is really a const function"

This reverts commit 0b66b481fe846e5f5d7122c6fe329e73ff79b051.

Again... @Dr15Jones does not agree as suggested in #230, hence I
revert it.
Merge pull request #231 from ktf/revert-getParameterNames-changes

Revert "getParameterSetNames is really a const function"